Sarcomere is the unit of
(a) Contraction
(b) Relaxation
(c) Contraction and relaxation
(d) None of the above

Options

A. Contraction
B. Relaxation
C. Contraction and relaxation
D. None of the above.

Answer

To solve the question regarding the function of a sarcomere, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Sarcomere**:
- A sarcomere is defined as the basic structural and functional unit of striated muscle tissue. It is the segment of a myofibril that lies between two Z lines.

2. **Identifying the Components**:
- Within a sarcomere, there are two types of filaments: thick filaments (myosin) and thin filaments (actin). These filaments are responsible for muscle contraction.

3. **Function of Sarcomere**:
- The primary role of the sarcomere is to facilitate muscle contraction. When a muscle contracts, the thick and thin filaments slide past each other, leading to a shortening of the sarcomere.

4. **Relaxation Process**:
- While relaxation occurs after contraction, it is not the primary function of the sarcomere. The sarcomere itself is not responsible for relaxation; it is primarily involved in the contraction process.

5. **Evaluating the Options**:
- (a) Contraction: Correct, as sarcomeres are the units that contract.
- (b) Relaxation: Incorrect, as sarcomeres do not function primarily in relaxation.
- (c) Contraction and relaxation: Incorrect, as the sarcomere is specifically the unit of contraction.
- (d) None of the above: Incorrect, since option (a) is correct.

6. **Conclusion**:
- Based on the above analysis, the correct answer is (a) Contraction.

### Final Answer:
(a) Contraction